Barrier discharge conversion of Hg, SO2 and NOx

ABSTRACT

A process and apparatus for reducing particulate, nitrogen oxides (&#34;NOx&#34;), sulfur dioxide (&#34;SO 2  &#34;), and mercury (&#34;Hg&#34;) emissions from the combustion exhaust of fossil fuel fired plants while producing an end product that is commercially useful, comprising the steps of oxidizing Hg, NOx and SO 2  using a barrier, pulse, corona, or electron beam electrical discharge apparatus (100) to produce HgO and the acids HNO 3  and H 2  SO 4  collecting the HgO, acids and particulates in a wet ESP (120), and separating the particulates from the collected acid mixture, then separating and concentrating the acids for industrial use.

This application claims the benefit of U.S. Provisional Application No.60/027,905, filed Oct. 9, 1996.

BACKGROUND

a. Field of the Invention

This invention relates to pollution control equipment used for reducingparticulate matter, nitrogen oxides ("NOx"), sulfur dioxide ("SO₂ "),and mercury ("Hg") emissions from the burning of fossil fuels.

b. Description of the Related Art

Electric utilities, and industrial plants typically burn fossil fuelslike coal to produce electric power and heat for process requirements.Burning fossil fuel produces an emissions stream containing a number ofnoxious substances as by-products. These substances include fineparticulate matter, mercury and oxides of nitrogen and sulfur. Fineparticulate matter has been shown in a recent study to contribute to theearly deaths of 64,000 people in the United States alone. Oxides ofnitrogen, generally known as NOx, result in the formation of groundlevel ozone, O₃, which is toxic when inhaled. Oxides of sulfur,generally known as SO₂, are also a problem. Both NOx and SO₂ compoundscontribute to the formation of acid rain, which is harmful to plantlife, animal life, and property. Mercury, in very small concentrations,has been shown to be highly toxic to humans.

The typical methods of reducing fine particulate matter emissions is bythe use of an electrostatic precipitator (ESP) or fabric filter baghouses. The typical methods of reducing SO₂ emissions are wet or dryscrubbers, burning low-sulfur coal, and employing flue gasdesulfurization (FGD) apparatuses. Burning low-sulfur coal reduces theparticulate collection efficiency of the ESP, and is generally moreexpensive than ordinary coal. FGD equipment is very expensive to buildand operate. The typical method of reducing NOx emissions is the use ofspecial low NOx burners to cool the combustion temperature to a pointwhere the bonds of N₂ present in the combustion air are less likely tobe broken. This has the disadvantage of making combustion less efficientand increases particulate emissions. Expensive selective catalytic andnon-catalytic reduction systems using ammonia and urea injection havealso been tried. These devices are very expensive to purchase andoperate. They can also require large amounts of space at the plant siteto install. Altogether, current methods for reducing fine particle, SO₂and NOx emissions can increase the cost of electricity produced at anelectric utility by over fifty percent.

Stauffer, in U.S. Pat. No. 4,925,639, that issued on May 15, 1990,disclosed a process for removing NOx from flue gas and making HNO₃ as auseful by-product. The process involved cyclically subjecting the gas toscrubbing with nitric acid and then electrolyzing the dissolved nitricoxide to form more nitric acid. This process has the disadvantage thatit only treats one type of pollution.

A few have tried to remove multiple pollutants from a flue gas stream.Plaks et al., in U.S. Pat. No. 5,601,791, that issued on Feb. 11, 1997,discloses a process and apparatus that neutralizes "acid gases" such asSO₂ inside an existing ESP. Plaks et al. spray a neutralizing agentupstream from the ESP collecting plates to collect particulates, neutralsalts, and unreacted neutralizing agent. The material collected on theplates is then washed using a spray in the manner of a wet ESP. Thisprocess and apparatus does not purposefully create and collect theacids, which are valuable industrial materials. Instead, the resultingeffluent is sent to a landfill for disposal.

Sparks et al., in U.S. Pat. No. 4,885,139, that issued on Dec. 5, 1989,discloses a method for removing SO₂ and other "acid gases" from flue gasby a multi-stage ESP within a single housing. In that method, aneutralizing agent is sprayed upstream from the ESP collecting plates,forming neutral salts which dry before being collected by the plates. Inthis manner SO₂ and particulates are removed from the flue gas. However,like Plaks et al., no effort is made to form H₂ SO₄ from the SO₂, andthe effluent must be sent to a landfill for disposal. Nor do either ofthem refer to the removal of NOx or the formation of HNO₃ in thismanner.

The deleterious health effects of these noxious pollutants become betterunderstood as more medical research is completed. As a result,environmental regulations world-wide are being made more stringent.Although mercury emissions from fossil fuel fired boilers are not yetregulated, this is likely to change as research has shown that over 20percent of mercury emissions in the United States come from coal firedpower plants. When the environmental regulations become more stringent,the cost of compliance increases. More expensive pollution controlequipment must be purchased and maintained which does not provide anymonetary return to the plant owner.

While environmental compliance costs continue to rise, there is amovement toward consolidating ownership of power plants world-wide andincreasing competition. As a result, capital expense budgets are oftenslashed in an effort to keep the cost of producing electricity low. Apollution control process and apparatus that can provide a monetaryreturn to the owner while reducing particulate, NOx, and SO₂ emissionswould solve several serious problems at the same time.

To date, a limited number of plants have been able to sell collectedparticulate matter commercially. Of the gases, only SO₂ has beenconverted to useful products that can provide a monetary return. It hasbeen used in the manufacture of gypsum and in the recovery of elementalsulfur. Also, dilute acids have been manufactured from exhaust gases bycatalytic reactions. These methods are limited, and are not widely used.

For the foregoing reasons, there is a need for a process and apparatusfor reducing particulate, NOx, and SO₂ emissions from the combustion offossil fuel while producing an end product that is commercially usefuland eliminating the need to dispose of an environmentally undesirableby-product.

SUMMARY

The present invention is directed to a process and apparatus thatsatisfies the need to reduce particulate, SO₂, NOx and Hg emissions fromcombustion of fossil fuel while producing a commercially useful endproduct. A process that reduces particulate, NOx, SO₂ and Hg emissionscomprises the steps of oxidizing NOx and SO₂ to produce the acids HNO₃and H₂ SO₄, and oxidizing Hg to HgO using a barrier, pulse, corona, orelectron beam electrical discharge apparatus, collecting the acids andparticulates in a wet ESP, separating the particulates from the wet ESPeffluent, then separating and concentrating the acids for industrialuse. The converting apparatus and wet ESP are preferably installedinside an existing ESP casing to conserve space. These and otherfeatures, aspects, and advantages of the present invention will becomebetter understood with reference to the following drawing anddescription.

DRAWINGS

FIG. 1 is a cut-away view of an ESP casing with the dry ESP sections,electrical converter, and wet ESP sections inside, and with the wet ESPeffluent separating and processing apparatuses shown in block diagramform.

FIG. 2 is a cut-away view like in FIG. 1 but showing more details.

FIG. 3 is a detail view of flat plate, barrier discharge electrodes.

FIG. 4 is a width-wise sectional view of a flat plate, barrier dischargeelectrode surrounded by high dielectric strength insulating material.

FIG. 5 is a length-wise sectional view of a flat plate, barrierdischarge electrode surrounded by high dielectric strength insulatingmaterial.

FIG. 6 is a side view of an electrode assembly having spaced electrodeconductors surrounded by high dielectric strength insulating material.

FIG. 7 is a perspective view of the electrical converter assembly stacksinside an ESP casing.

FIG. 8 is a process diagram of the processing apparatus for separatingand concentrating HNO₃ and H₂ SO₄.

DESCRIPTION

The present invention is a process and apparatus for reducingparticulate, NOx, (including NO₂), SO₂ and Hg emissions from thecombustion exhaust of fossil fuel fired plants which producescommercially valuable acids as reaction products. Turning to FIG. 1,flue gas 10 is created by the combustion of fossil fuel in a boiler.Fuels that are typically used in electric utilities and industrialplants include coal and oil, but may comprise other substances like gas,tires, trash, or biomass. Flue gas 10 enters an electrostaticprecipitator casing (ESP) 15 and a standard dry ESP 14 removesapproximately 90% of the particulate ash.

In the preferred embodiment, the last fields of the existing dry ESP areremoved to make room for the electrical converting apparatus 100 and wetESP section 120. The converting apparatus 100 oxidizes NOx, SO₂, and Hgpresent in the flue gas to HNO₃, H₂ SO₄, and HgO. The acids, and most ofthe fine particles not collected by the dry ESP 14 are collected in thewet ESP 120. The wet ESP 120 also collects HgO, NO₂ gas, and SO₂ gas.Having had most of the NOx, SO₂, and particulate matter removed, theflue gas exits the precipitator at 20 with greatly reduced amounts ofNOx, SO₂, and Hg and almost no particles. As an alternative to thepreferred embodiment, the converter 100 and wet ESP 120 can be installedoutside the existing ESP casing 15. Yet another alternative is to followthe converter 100 and wet ESP 120 sections with an additional converterand wet ESP section, either inside or outside the ESP casing 15, inorder to obtain a desired conversion efficiency.

The effluent from the wet ESP 120 is collected in a collection hopper asa mixture and travels to a separator apparatus 140, where theparticulates and HgO 144 are removed. The separator apparatus maycomprise a settling tank, a filter, a centrifuge, or any combination ofthe three as is commonly practiced in the art. A mineral removalapparatus may be used to remove HgO from the mixture.

The remaining mixture travels to a processing apparatus 160, thatseparates the HNO₃ and H₂ SO₄, and concentrates them for industrial use.The result is concentrated H₂ SO₄ 200 and concentrated HNO₃ 210.

Turning to FIG. 2, the composition of the flue gas 12 before the dry ESP14 is primarily particulate ash, N₂, CO₂, H₂ O, O₂, SO₂, NOx, Hg andother trace heavy metals. After the dry ESP 14 and before the converterapparatus 100, the composition of the flue gas 16 is primarily fineparticles, N₂, CO₂, H₂ O, O₂, SO₂, NOx, Hg and other trace heavy metals.

The electrical converter apparatus 100 is a series of flat plate,barrier discharge electrodes formed in stacks 106. The electrodes areenergized by a power supply 102 that converts station-provided,three-phase power into high voltage alternating current power. The powersupply is electrically connected to the converter apparatus. The voltagesupplied to the converter is preferably between about 15,000 and about50,000 volts root mean square (RMS) at a frequency between about 50 Hzand about 10 kHz. The preferred embodiment operates at about 1 kHz.Operating at a higher frequency reduces the size and cost of the highvoltage transformer required.

In using barrier electrical discharge, high voltage alternating currentis applied to electrodes which are separated by a gas space and adielectric barrier. The voltage can be applied in any one of severalwaveforms, including but not limited to sine, square, triangle, andpulsed voltages. Other types of electrical discharge apparatuses thatmay be employed for converting NOx and SO₂ to acids include, but are notlimited to, pulse, corona, and electron beam discharge and radiofrequency, microwave, and ultraviolet light radiation sources. Neitherbarrier electrical discharge nor the other named energy sources havebeen used to reduce both NOx and SO₂ in the fossil fuel boilers ofelectric utilities and industrial plants before. That it is useful inthese applications is surprising and unexpected.

The major chemical reactions in the conversion of NOx to HNO₃ are asfollows:

(1) O₂ +e→O+O+e

(2) H₂ O+e→OH+H+e

(3) NO+O→NO₂

(4) NO₂ +O→NO₃

(5) NO₂ +OH→HNO₃

(6) NO₃ +NO₂ →N₂ O₅

(7) N₂ O₅ +H₂ O→2HNO₃

The major chemical reactions in the conversion of SO₂ to H₂ SO₄ are asfollows:

(1) SO₂ +O→SO₃

(2) SO₂ +OH→HSO₃

(3) HSO₃ +OH→H₂ SO₄

(4) SO₂ +HO₂ →HSO₄ →H₂ SO₄

(5) SO₃ +H₂ O→H₂ SO₄

The composition of the flue gas 18 after the electrical converter butbefore the wet ESP 120 is primarily fine particles, N₂, CO₂, H₂ O, O₂, afraction of the original SO₂, a fraction of the original NOx(predominantly in the form of NO₂), HgO, H₂ SO₄ and HNO₃. Note that theconverter apparatus 100 converted Hg present in the flue gas to HgO thatis readily collected in the wet ESP 120.

An evaporative cooling spray injection apparatus 122 sprays water, anacid mixture, or both into the flue gas just before it reaches the wetESP 120. This spray acts to cool the flue gas to a temperature below thesulfuric and nitric acid dew points so that acid aerosols will form inthe gas stream. This permits subsequent collection of acids in the wetESP section. Spraying a dilute nitric and sulfuric acid spray alsoscrubs additional SO₂ and NO₂ from the flue gas. Like the dry ESP 14,the wet ESP 120 comprises a plurality of plates 128 between which arehigh voltage, preferably rigid, electrodes. In the preferred embodiment,the plates are sub-cooled below the temperature of the flue gas, forexample, by the use of cooling water 124 provided at the station. Inthis manner the acids in the composition of the flue gas 18 tend tocondense on the surfaces of the wet ESP plates 128. This apparatus isknown as a "condensing" wet ESP. Very little of the pollutants in thecomposition of the flue gas 18 exit the ESP 120 and go into theenvironment through the stack 22.

The effluent 126 from the wet ESP is primarily a slurry or mostly-liquidmixture of dilute H₂ SO₄, dilute HNO₃, scrubbed SO₂, fine particles, andHgO. It travels to a separation apparatus 140. The mixture is separatedby a settling tank, centrifuge, or filter 142. The resulting solids 144are removed and safely disposed of or recycled. The remaining diluteacids 148 are transported by an optional pump 146 to a processingapparatus 160 that separates the acids and concentrates them to produceHNO₃ 210 and H₂ SO₄ 200.

FIG. 3 shows a converter cell comprising a high voltage, flat plateelectrode 101 connected to the high voltage power supply 102 (not shown)secured at a distance from two flat plate grounded electrodes 103.Although the flat plate electrode configuration is the preferredembodiment, other embodiments are also possible. They includecylindrical high voltage electrodes and flat plate ground electrodes,and cylindrical high voltage electrodes centered in the middle ofcylindrical ground electrodes. The plates are preferably mounted in avertical position to prevent plugging with particulate matter. The highvoltage electrodes 101 and ground electrodes 103 may have identicalconstruction, and differ only in that one is wired to the power supply102 and the other is wired to ground. In operation, the high voltage andground electrodes would alternate along the entire row, and have groundelectrodes at the end. Another configuration is to have alternatingelectrodes attached to opposite ends of the secondary windings of a highvoltage, mid point ground transformer. The significant requirement isthat a high voltage gradient exist between the electrodes.

FIGS. 4 and 5 are cut-away sectional views of the preferred flat plateelectrodes. The electrode itself 112 may be made of any conductivemetal. Instead of using flat plates, conductive wire mesh screens,conductive inks or epoxy strips may also be used. The high dielectricbarrier 114 is important for providing sufficient energy to convert NOxand SO₂ into the chemical species that will result in the formation ofHNO₃ and H₂ SO₄. The high electric material is applied over all thesurfaces of the electrodes. The preferred embodiment uses mica as thedielectric material. However, quartz, alumina, titania, fused silica,and ceramic may also be used.

FIG. 6 is an alternative to the flat plate electrode 112. Thisembodiment uses a flat, spaced electrode conductor 116 surrounded by thehigh dielectric barrier 114.

FIG. 7 shows a perspective view of converter stack assemblies 106a,106b, and 106c installed inside a precipitator casing 15. The assembliescomprise short rows of plates, preferably about 90 cm in length, withthe plates preferably spaced from each other by about 1.3 cm. The platesthemselves are preferably about 104 cm in height and less than about 30cm in width. The plates are high voltage plates 101 and either ground oropposite polarity high voltage plates 103. The arrangement of the platesmay comprise alternating ground 103 and high voltage plates 101,alternating across the rows with ground plates 103 on the end.Alternatively, each high voltage plate 101 may be surrounded by twoground plates 103 on either side.

The rows are supported by a mechanical structure (not shown) andsuspended by insulators 108a and 108b from the top of the casing 15 sothat the plane of the plates is parallel to the flow direction of theflue gas within the casing. In this manner, a maximum amount of the fluegas is treated by the converter with a minimum pressure drop across theapparatus. A plurality of rows may be mechanically fastened together,one on top of the other, to form a stack 106 that reaches substantiallyfrom the top to the bottom of the casing, which is typically about nineto about twelve meters in height. Although not shown, the plates of eachrow, and each row, are electrically connected to provide the desiredinput power from the power supply 102.

A plurality of stacks 106 may be used and installed side by side tosubstantially cover the width of the casing. The number of plates, rows,and stacks shown in FIG. 7 are for illustration only, and it isappreciated that different quantities of plates, rows, and stacks may berequired for different sized casings.

FIG. 8 is a schematic diagram of the preferred embodiment of aprocessing apparatus 160 for separating and concentrating HNO₃, and H₂SO₄ from the dilute acids 148 output from the separator 140. Theschematic only shows the mass flow, and not the energy flow, but it isunderstood by those skilled in the art that heat exchangers andcondensers can be used in these apparatuses to facilitate the desiredseparation and concentration of acids. Other apparatuses and processesare also suitable for separating and concentrating the acids, as isunderstood by those skilled in the art. The elements are hydraulicallyconnected, in that fluids may be conveyed by acid-resistant pipes,hoses, and containers. Pumps are shown in various places, however theyare optional and could be replaced by gravity feed or other fluidconveying means.

In FIG. 8, the preferred embodiment processing apparatus 160 has threedistinct sections: a denitration apparatus 170, H₂ SO₄ concentrationapparatus 180, and HNO₃ concentration apparatus 190. In the denitrationapparatus 170, the dilute acids 148 enter a processing tower 172 thathas two outputs. A first output is hydraulically connected to astripping column 174 input. The stripping column 174 output ishydraulically connected to a pump tank 176 input. The pump tank 176output is hydraulically connected to an acid pump 178 input. From theacid pump 178 output flows weak, denitrated H₂ SO₄ 181.

In the H₂ SO₄ concentration apparatus 180, weak denitrated H₂ SO₄ 181flows into a separator 182 having two outputs. The separator 182 inputis hydraulically connected to the denitration unit acid pump 178 output.The separator 182 first output is hydraulically connected to a transferpump 184 input. The transfer pump 184 output is hydraulically connectedto a pump tank 186 input. The pump tank 186 output is hydraulicallyconnected to an acid pump 188 input. From the acid pump 188 output comesconcentrated H₂ SO₄ 200, suitable for industrial use. Distillate H₂ O183 flows from the separator 182 second output.

In the HNO₃ concentration apparatus 190, concentrated H₂ SO₄ 200 entersa first input of a processing tower 192. The processing tower 192 firstinput is hydraulically connected to the H₂ SO₄ concentration apparatusacid pump 188 output. The processing tower 192 second input ishydraulically connected to the denitrating apparatus processing tower172 second output to supply weak HNO₃ to the HNO₃ concentrationapparatus 190. From a second output of the processing tower 192 comesconcentrated HNO₃ 210, suitable for industrial use. The processing tower192 first output is hydraulically connected to a stripping column 194input. The stripping column 194 output is hydraulically connected to apump tank 196 input. The pump tank 196 output is hydraulically connectedto an acid pump 198 input. The acid pump 198 output is hydraulicallyconnected to the H₂ SO₄ concentration apparatus separator 182 input.

It will be apparent to those skilled in the art that various changes andmodifications can be made without departing from the spirit of thepresent invention. Accordingly, it is intended to encompass within theappended claims all such changes and modifications that fall within thescope of the present invention.

We claim:
 1. A process for removing particulate, Hg, NOx, and SO₂emissions from a flue gas stream and collecting the resulting acids forindustrial use comprising the steps ofa. oxidizing Hg, NOx and SOx in aflue gas stream using an electrical converting apparatus to HgO, HNO₃and H₂ SO₄ ; b. collecting particulate emissions, HgO, NO₂, SO₂, HNO₃,and H₂ SO₄ in a wet electrostatic precipitator (ESP), forming a mixture;c. separating the particulate emissions and HgO from the mixture; and d.processing the mixture by separating HNO₃ and H₂ SO₄ from each other andconcentrating HNO₃ and H₂ SO₄, and thereby removing particulate, Hg,NOx, and SO₂ emissions from the flue gas stream and producing acids forindustrial use.
 2. The process of claim 1, wherein the electricalconverting apparatus is at least one taken from the group consisting ofbarrier, pulse, corona, and electron beam electrical discharge sourcesand radio frequency, microwave, and ultra-violet light radiationsources.
 3. The process of claim 1, further comprising the step ofcollecting particulate emissions with a conventional electrostaticprecipitator located upstream from the electrical converting apparatus.4. The process of claim 1, wherein the oxidizing step comprisesoxidizing NOx and SO₂ using a barrier discharge to initiate the chemicalreactions resulting in the formation of HNO₃ and H₂ SO₄.
 5. The processof claim 4, wherein the oxidizing is performed using a high voltage,alternating current power source at a frequency between about 50 Hz andabout 10 kHz.
 6. The process of claim 4, wherein the oxidizing isperformed at an input of between about 15,000 volts and about 50,000volts RMS.
 7. The process of claim 1, wherein the wet electrostaticprecipitator is a condensing wet electrostatic precipitator having atleast one collecting plate having two surfaces, said plate comprising amechanism for cooling the surfaces of the plate.
 8. The process of claim7 further comprising the steps of injecting an evaporative cooling sprayof a dilute HNO₃ and H₂ SO₄ mixture upstream from the collecting plate;sub-cooling the surfaces of the plate below the temperature of the fluegas; condensing H₂ O, HNO₃ and H₂ SO₄ onto the plate surfaces forming acondensate; and entraining particulate emissions in the condensate,forming a mixture.
 9. The process of claim 1, the collecting stepcomprising the step of scrubbing SO₂ and NO₂ from the flue gas stream inthe wet ESP.
 10. The process of claim 1, the separating step comprisingthe step of removing the HgO from the mixture using a mineral removalapparatus.
 11. An apparatus for removing particulate, Hg, NOx, and SO₂emissions from a flue gas stream and collecting the resulting acids forindustrial use comprisinga. an electrical converting apparatus installedwithin an electrostatic precipitator casing for converting Hg, NOx andSO₂ to HgO, HNO₃ and H₂ SO₄ ; b. a wet electrostatic precipitator havinga collection hopper installed within the casing downstream of theelectrical converting apparatus for collecting particulates, HgO, HNO₃and H₂ SO₄ in a mixture; c. a separating apparatus outside the casinghydraulically connected to the collection hopper for separating theparticulates and HgO from the HNO₃ and H₂ SO₄ in the mixture; and d. aprocessing apparatus hydraulically connected to the separating apparatusfor separating HNO₃ and H₂ SO₄ from each other and concentrating HNO₃and H₂ SO₄, thereby removing particulate, Hg, NOx, and SO₂ emissionsfrom the flue gas stream and producing acids for industrial use.
 12. Theapparatus of claim 11, wherein the electrical converting apparatus istaken from a group consisting of barrier, pulse, corona, and electronbeam electrical discharge sources.
 13. The apparatus of claim 11,wherein the electrical converting apparatus is taken from a groupconsisting of radio frequency, microwave, and ultra-violet lightradiation sources.
 14. The apparatus of claim 11, further comprising aconventional electrostatic precipitator located within the casing andupstream from the electrical converting apparatus.
 15. The apparatus ofclaim 11, wherein the electrical converting apparatus is a barrierdischarge excitation apparatus that oxidizes NOx and SO₂ and initiatesthe chemical reactions resulting in the formation of HNO₃ and H₂ SO₄.16. The apparatus of claim 15, wherein the barrier discharge excitationis performed by a high voltage, alternating current power source at afrequency between about 50 Hz and about 10 kHz.
 17. The apparatus ofclaim 15, wherein the barrier discharge excitation is performed at aninput of between about 15,000 volts and about 50,000 volts RMS.
 18. Theapparatus of claim 15, wherein the barrier discharge excitationapparatus comprises a high voltage, alternating current power source;electrically connected to at least one high voltage electrode surroundedby a high dielectric barrier; secured at a distance from at least onegrounded electrode.
 19. The apparatus of claim 18, wherein the highvoltage and ground electrodes are substantially parallel sheets ofelectrically conductive material, and the high dielectric barrier ismade of a material taken from the group consisting of glass, fusedsilica, ceramic, and mica.
 20. The apparatus of claim 19, wherein thehigh voltage and ground electrodes are substantially parallel screenplates.
 21. The apparatus of claim 19, wherein the high voltage andground electrodes are substantially parallel planar spaced stripconductors.
 22. The apparatus of claim 11, wherein the wet electrostaticprecipitator is a condensing wet electrostatic precipitator having atleast one collecting plate having two surfaces, said plate comprising amechanism for cooling the surfaces of the plate.
 23. The apparatus ofclaim 22, further comprising an evaporative cooling spray injectionsystem upstream from the collecting plate for cooling the flue gastemperature below the dew point for HNO₃ and H₂ SO₄ ; scrubbing SO₂,NO₂, and HgO from the gas stream; condensing water, HNO₃ and H₂ SO₄ ontothe plate surfaces forming a condensate; and entraining particulateemissions in the condensate, forming a mixture.
 24. The apparatus ofclaim 11, wherein the separating apparatus is at least one taken from agroup consisting of a filter, a settling tank, and a centrifuge.
 25. Theapparatus of claim 11, said processing apparatus for separating HNO₃ andH₂ SO₄ from each other and concentrating HNO₃ and H₂ SO₄ comprising adenitration apparatus, an H₂ SO₄ concentration apparatus, and an HNO₃concentration apparatus.
 26. The apparatus of claim 25, said denitrationapparatus for producing denitrated H₂ SO₄ comprising a processing towerhaving an input and a first and second output, the processing towerinput hydraulically connected to the separating apparatus; a strippingcolumn having an input and an output, the stripping column inputhydraulically connected to the processing tower first output; a pumptank having an input and an output, the pump tank input hydraulicallyconnected to the stripping column output; and an acid pump having aninput and output, the acid pump input hydraulically connected to thepump tank output, thereby producing denitrated H₂ SO₄ from the acid pumpoutput.
 27. The apparatus of claim 26, said H₂ SO₄ concentrationapparatus comprising a separator having an input, a first output and asecond output, the separator input hydraulically connected to the outputof the denitration apparatus acid pump; a transfer pump having an inputand an output, the input of the transfer pump hydraulically connected tothe separator first output; a pump tank having an input and an output,the input of the pump tank hydraulically connected to the output of thetransfer pump, and an acid pump having an input and an output, said acidpump input connected to the pump tank output, thereby producingconcentrated H₂ SO₄ from the acid pump outlet, and distillate H₂ O fromthe separator second output.
 28. The apparatus of claim 27, said HNO₃concentration apparatus comprising a processing tower having a first andsecond input and a first and second output, the processing tower firstinput hydraulically connected to the H₂ SO₄ acid pump outlet, theprocessing tower second input hydraulically connected to the denitrationapparatus processing tower second output; a stripping column having aninput and an output, the stripping column input hydraulically connectedto the processing tower first output; a pump tank having an input and anoutput, the pump tank input hydraulically connected to the strippingcolumn output; and an acid pump having an input and an output, the acidpump input hydraulically connected to the pump tank output, and the acidpump output hydraulically connected to the denitration apparatus acidpump output, thereby producing concentrated HNO₃ from the processingtower second output.